The present disclosure relates to a transverse electric field type liquid crystal display device. Specifically, the disclosure relates to a transverse electric field type liquid crystal display device capable of achieving an increase in the angle of view by using two negative biaxial films as retardation plates.
Liquid crystal display devices have characteristics of a light weight, a small thickness, and low power consumption as compared with CRTs (Cathode-Ray Tube), and thus are used for display in many electronic apparatuses. The liquid crystal display device displays an image by changing a direction of liquid crystal molecules oriented in a prescribed direction through an electric field so as to change an amount of light transmitted through a liquid crystal layer. As a method of applying an electric field to the liquid crystal layer of the liquid crystal display device, there are methods using a vertical electric field type and a transverse electric field type. In the liquid crystal display device of the vertical electric field type, an electric field is applied to liquid crystal molecules in a substantially vertical direction by using a pair of electrodes which are disposed with a liquid crystal layer interposed therebetween. Examples of the known liquid crystal display device of the vertical electric field type include liquid crystal display devices of a TN (Twisted Nematic) mode, a VA (Vertical Alignment) mode, an MVA (Multi-domain Vertical Alignment) mode, and the like.
In the transverse electric field type liquid crystal display device, a pair of electrodes are disposed to be insulated from each other on the inner side of one substrate of a pair of substrates which are disposed with a liquid crystal layer interposed therebetween, and an electric field in the substantially vertical direction is applied to the liquid crystal molecules. Examples of the known transverse electric field type liquid crystal display device include liquid crystal display devices of an IPS (In-Plane Switching) mode, in which the pair of electrodes do not overlap each other in plan view, and a FFS (Fringe Field Switching) mode in which the pair of electrodes overlap each other. The transverse electric field type liquid crystal display devices have an effect of achieving a wide angle of view, and thus recently have come into widespread use.
The transverse electric field type liquid crystal display device uses liquid crystal, which is homogeneously aligned, and a pair of polarizing plates which are disposed with the liquid crystal layer interposed therebetween such that the transmission axes thereof are orthogonal to each other in vertical and horizontal directions with respect to a front side of a screen. In the transverse electric field type liquid crystal display device having such a configuration, as the screen is viewed at an angle from the left, right, top, or bottom, the two transmission axes have a positional relationship that those are orthogonal to each other, and thus it is possible to obtain a sufficient contrast. However, as the screen is viewed at an azimuthal angle of 45°, an angle formed between the transmission axes of the pair of polarizing plates is larger than 90°. Therefore, the transmitted light leaks due to birefringence thereof, and thus the contrast is lowered. Accordingly, there are problems such as a decrease in the angle of view caused by the deterioration in contrast.
As liquid crystal display devices for solving the problems of the transverse electric field type liquid crystal display devices, in the related art, there have been known liquid crystal display devices using various retardation plates and the like for the sake of increasing an angle of view or improving image quality. For example, Japanese Patent No. 3118208 discloses a liquid crystal display device that has an optical compensation sheet which has an optically negative uniaxiality. Further, Japanese Patent No. 3204182 discloses a liquid crystal display device that has two layers, each of which has a positive uniaxial optical anisotropy, as compensation layers for compensating a birefringent index of the liquid crystal layer.
Furthermore, PCT Japanese Translation Patent Publication No. 2006-520008 discloses a liquid crystal display device using a negative biaxial retardation film and a +C-plate as films for compensating the angle of view. In addition, Japanese Unexamined Patent Application Publication No. 2006-293108 discloses a liquid crystal display device using a negative uniaxial optical film, which has an optical axis in a plane thereof, and a second optical film (a negative biaxial optical film) of which the refractive index in a thickness direction is smaller than any direction in the plane thereof.
Further, Japanese Patent No. 4276392 discloses a liquid crystal display using a C-type or P-type wide-viewing-angle polarizing plate. Here, the C type is a wide-viewing-angle polarizing plate formed by overlapping, in an orthogonal manner, biaxial retardation films each of which has a birefringence characteristic that a phase difference in the plane of the polarizer is equal to 250 nm to 300 nm and Nz is equal to 0.1 to 0.4. The P type is a wide-viewing-angle polarizing plate formed by overlapping, in a parallel manner, the biaxial retardation films each of which has a birefringence characteristic that a phase difference in the plane of the polarizer is equal to 250 nm to 300 nm and Nz is equal to 0.6 to 1.1.